ROLE OF THE OLIVO-CEREBELLAR NETWORK IN MOTOR COORDINATION AND LEARNING The goal of this research project is to define the dynamic properties of the olivo-cerebellar circuit, in the context of the physiological properties of single cells and of the neuronal connectivity they support. In particular, the electrophysiology of inferior olive (IO)neurons, and Purkinje cells (PC)and their connectivity, will be examined. Four interrelated specific aims, utilizing pharmacological or molecular biological interventions relating to calcium channel ionic conductances will be implemented. Specifically, we will study the role of CaV2.1 (formerly D1A) and CaV3.1 (formerly D1G) channels in the organization of the olivo-cerebellar system by determining: 1. The in vitro effect of pharmacological block of these channels on IO electrophysiological properties and on the IO ensemble properties using voltage dependent dye imaging. 2. The in vitro effect of molecular biological modifications of CaV 2.1 and CaV 3.1 on IO and PC electrophysiology using patch recording and of IO ensemble properties using voltage dependent dye imaging 3. The in vivo characterization of the pharmacologically and molecular biologically modified IO cellular properties on the system dynamics of the olivo-cerebellar system with respect i) spontaneous and evoked complex spike PC activity in the cerebellar cortex using multiple electrode voltage recording, ii) Properties of vibrissal movement using motor cortex stimulation and iii) two-photon transcranial calcium dependent imaging of spontaneous and sensory evoked PC activity at the cerebellar cortex. 4. Motor skills acquisition abilities (rotorod test) and motricity/postural compensation properties following unilateral vestibular lesion. In addition, knockout mice will be examined morphologically to determine, quantitatively, the residual presence of the CaV2.1 and CaV3.1 channel moiety utilizing immunohistochemical localization at the IO and cerebellar neurons. From a clinical perspective, IO neuronal properties have been related directly to such neurological conditions as Essential Tremor. Indeed, octanol, a specific blocker of CaV3.1 in the IO neurons is presently being considered for therapeutic use in this neurological condition in humans.